Comparative in vitro Efficacy of Synthetic and Biological Fungicides Against Colletotrichum and Fusarium Infecting Black Pepper (Piper nigrum L.) in Côte d’Ivoire

Abstract

Aims: Black pepper (Piper nigrum L.) is gaining importance in agricultural systems due to the nutritional and medicinal value of its berries. However, its cultivation is increasingly threatened by fungal diseases, primarily caused by Colletotrichum and Fusarium species, resulting in substantial yield losses in several producing regions, including Côte d’Ivoire. Study Design: This study evaluated the in vitro efficacy of nine synthetic fungicides and three biological formulations on mycelial growth, sporulation, and spore germination of these pathogens. Place and Duration of Study: The in vitro assay was conducted in the Plant Pathology and Plant Biology Laboratory at UMRI-SAPT, Institut National Polytechnique Félix HOUPHOUËT-BOIGNY, Côte d’Ivoire. Methodology: The study evaluated the in vitro efficacy of nine synthetic fungicides and three biological formulations on the mycelial growth, sporulation, and spore germination of these pathogens at three tested concentrations (D1 = ½ the recommended dose, D2 = the recommended dose, D3 = 2× the recommended dose). Results: Several synthetic fungicides — chlorothalonil, carbendazim, carbendazim + mancozeb, azoxystrobin + mancozeb, picoxystrobin + mancozeb, and difenoconazole + spiroxamine—completely or significantly inhibited the growth of both fungal genera at all tested concentrations. Among biological products, the formulation Thymol–Gamma terpinene–Eugenol (NECO) fully suppressed the mycelial growth of Colletotrichum and Fusarium isolates at 80 mL/L (D2) and 160 mL/L (D3). In contrast, Lippia multiflora essential oil exhibited a dose-dependent inhibitory effect (12.5, 25, and 50 mL/L). In contrast, the aqueous extract of Chromolaena odorata displayed limited activity. Conclusion: These findings highlight the potential of biopesticides—particularly Lippia multiflora essential oil and NECO formulation—as promising alternatives for integration into sustainable management programs against fungal diseases of black pepper. Further field studies are required to validate their performance and optimize application strategies for local production systems in Côte d’Ivoire.